Prosthesis interface surface and method of implanting

ABSTRACT

An improved prosthesis interface surface is incorporated on any implantable component where stable long lasting bone fixation is needed. The surface achieves immediate stabilization of the prosthetic component and promotes bony tissue ingrowth by either making the surface of a porous metal or ceramic or coating the surface of the interface surface with a porous metal or ceramic. In the preferred embodiment, the surface includes a large number of conical protrusions which are specifically designed to resist shear and torsional disruptive forces while accommodating the compression loads that occur during motion of a joint prosthesis. By utilizing a series of conical protrusions, the surface contact area of the interface surface is much greater than interface surfaces now in use and this large surface contact area improves stability and provides a large area for secure bony ingrowth fixation. The improved prosthesis interface surface of the present invention may be used in hip, knee, ankle and shoulder joint replacement components as well as in any other implant component which is to be secured in trabecular bone. Additionally, the interface surface may be used to implant artificial dentures and for bony insertions of artificial ligaments and tendons. In another aspect of the present invention, a method of implanting artificial joints utilizing the improved prosthesis interface surface includes in one embodiment the use of a drill guide and in another embodiment a pilot driver.

This is a division of application Ser. No. 555,812, filed Nov. 28, 1983,now U.S. Pat. No. 4,659,331, and assigned to the assignee hereof.

BACKGROUND OF THE INVENTION

This invention relates to an improved prosthesis interface surface andthe method of implanting it in conjunction with an artificial jointreplacement procedure. At present, the majority of total jointcomponents are stabilized with methyl methacrylate bone cement whichfunctions as a mechanical interlock between the associated bone and thereplacement joint. Most of these total replacement prostheses have beenfor hip and knee joints and the designs utilized involve combinations ofplates, stems and/or peg structures to achieve fixation. Since thereplacement joints have little or no inherent stability without cement,the usual insertion procedures include production of oversized holes andfilling the holes with cement during implantation. Several disadvantagesof implants which require cement have been documented as follows:

(1) The single most frequent failure mode of cemented implants hasinvolved the loosening and subsequent failure thereof. While the rate ofloosening varies with component design and surgical techniques,loosening has universally been reported to be a major limiting factor tolong term success of the implant.

(2) The major disadvantages with cemented implant designs are: looseningor fragmentation at the bone-cement or prosthesis-cement interface;difficulty in removing cement in affected patients or in previousreplacement failures that need revision; poor mechanical properties ofmethyl methacrylate cement in that while it resists compression well, itresponds poorly to torsion, shear and tension; susceptibility of blood,fluids or air to be trapped in the cement to thereby cause stress risersand thus reduce fatigue strength; difficulty in controlling penetrationof the cement--while recent work has shown that pressurizing the cementimproves fixation to trabecular bone, the preparation of a cleantrabecular bone surface is critical and is difficult to achieve; theenlarged opening required for cement insertion requires the sacrifice ofa substantial amount of trabecular bone; and the physiological affectsof methyl methacrylate cement which in operation is a thermo settingacrylic are still as yet unknown.

A second class of prosthesis interface is designed to be used with noassociated cement. This class includes several hemiarthroplasties of thehip as well as the total knee tibial component which comprises apolyethylene structure with two large pegs. The pegs are driven intoundersized holes and include fins thereon which are designed to providestable fixation of the implant. The main draw back to these interferencefit type designs is the fact that they utilize large protrusions, suchas, stems or pegs which may concentrate stress in some areas and causestress relief in others. Bone remodeling responses to these stresspatterns may cause disadvantages bone substance reorientation andsubsequent failure of both the bone and the implant.

A further and more recent class of implants have been developed whichinclude a porous surface coating made from porous metal, polyethylene orceramic materials. These implants have been used as hip and knee jointreplacements as well as in conjunction with fixture of dentures.Basically, this class of devices has similar design to that of cementedimplants except that a porous material is used at the interface. Whilethe porous implants have not been use long enough to provide goodstatistical evaluations, several disadvantages have become evidentrecently:

(1) Bony ingrowth into the surface of the prosthesis has been reportedto occur only if the implants are extremely stable and secured for threeto eight weeks. In situations where movement of the components hasoccurred, a fibrous interface may form on the bone and thus cause aloose component. If this occurs, post-operative patient mobility may beseverely compromised.

(2) The prosthesis as presently designed needs an extremely accurateinitial fit and as such require tedious and sometimes difficult surgicaltechniques to achieve such a fit.

(3) The geometries of present implant designs do not optimize ormaximize the potential porous surfaces and thus limit the amount of bonyingrowth to a limited surface area which reduces the strength of thebond between the implant and the associated bone.

A further group of components include designs which utilize screws orstaples to augment the fixation thereof. Additionally, artificialligaments have been designed which contain metallic bony insertions.These components have disadvantages as requiring accuracy in fabricatingthe screw holes or the receiving surfaces for the staples and furtherthe screws may act to crack the bone tissue.

Applicants are aware of the following prior art:

U.S. Pat. No. 2,910,978 to Urist discloses a hip socket having aplurality of anchoring spikes 19 which project the exterior bottom ofthe shell 15. The spikes 19 provide a simple interference fit as thesole means for maintaining the socket in position. The device of Uristis different from applicants' invention because, firstly, in applicants'invention, the interference fit is only used on a temporary basis whilethe bony growth is forming; secondly, the device of the presentinvention provides a contact stress spectrum or gradient to assure anoptimum ingrowth environment. This contact stress gradient is a designfeature determinate for the shape, size and array of cones, a conceptnot confronted by Urist; thirdly, the device of the present invention isnot limited to hip implants but rather is applicable for any type ofprosthetic body implant.

U.S. Pat. No. 3,683,421 to Martinie discloses a prosthetic jointassembly wherein the bone attachment socket is provided with a pluralityof apparently conical projections 62 (FIG. 4) which are designed to morefirmly secure the socket to the associated acrylic cement. The patent toMartinie is obviously quite different to the teachings of the presentinvention since there is no disclosure therein of porous coatings, boneingrowth, contact stress or sequence of interference in permanentingrowth fixation.

U.S. Pat. No. 3,728,742 to Averill discloses a knee or elbow prosthesisincluding a bone contact surface which is provided with serrations 32 toassist in the firm anchorage by the associated cement. As is seen inFIG. 6 of Averill, the serrations are in no way related to theconfiguration of the surface of the present invention. Further, there isno disclosure in Averill of the concept of ingrowth of bony tissue.

U.S. Pat. No. 3,808,606 to Tronzo discloses a plurality of embodimentsof bone implants wherein a porous exterior surface is provided to permitingrowth of bone for secure fixation. As disclosed therein the porousexterior surface may be made of stainless steel, titanium or titaniumalloys which may be applied as a powder and then sintered, if desired.The present invention differs from Tronzo in that (1) Tronzo does notdisclose a configuration of conical projections like that of the presentinvention, (2) Tronzo does not treat a specific design or contact stresson the associated bones, (3) Tronzo does describe the use of aninterference fit preliminary to ingrowth fixation but differs in the waythat this is accomplished and (4) No provision is made for an optimalinterface between the prosthesis and the associated bone.

U.S. Pat. No. 3,860,731 to Waugh, et al. discloses a tibial implantincluding concentric rings which bite into the tibial bone. There is nodisclosure in this patent of ingrowth or a porous coating to facilitatebony ingrowth. The concentric rings as best shown in FIG. 7 bear noresemblance structurally or functionally to the teachings of the presentinvention.

U.S. Pat. No. 4,021,864 to Waugh discloses an ankle prosthesis includinga tibial member provided with truncated pyramidal teeth 20 best shown inFIGS. 6 and 7 which enhance the retention in the bone in conjunctionwith a suitable bone cement. Obviously there is no concept disclosed inWaugh of the use of a porous prosthetic surface to facilitate the bonyingrowth nor any disclosure of the specific structure disclosed in thepresent invention.

U.S. Pat. No. 4,166,292 to Bokros discloses a stress reinforcedartificial joint prosthesis made preferably of graphite with a pyrolyticcarbon coating. As shown, the prosthesis includes ridges 24 oftriangular cross-section which are provided to enhance the permanentfixation of the prosthesis. It is believed that the use of the graphitesubstrate is more related to a concept of shock absorption or trying tomatch the prosthetic elastic modulus or stiffness to that of the bone.This concept in no way relates to ingrowth fixation, a spectrum ofcontact stress or any other concepts disclosed herein.

U.S. Pat. No. 4,231,120 to Day discloses an endoprosthetic orthopedicdevice having a method of securement involving an elongated stem withannular or helical fin-like elements extending radially outwardlytherefrom. This device is inserted into a slightly undersized recess inthe bone and the fins provide fixation therein. With regard to thispatent, it is noted that no use of porous coated metal is describedtherein. True ingrowth into 100 to 400 micron pores is not used. Theprosthetic component of Day is made of polyethylene and the fixationtechnique described therein involves deformation of this largepolyethylene peg.

U.S. Pat. No. 4,309,777 to Patil discloses an artificial intervertebraldisc employing spikes 18 and 22 on the upper and lower surfaces thereoffor engagement with the respective vertabra. Springs 16 within thedevice provide the force necessary to insert the spikes in the vertebra.With regard to Patil, the above described projections are not coatedwith any porous material and rely solely upon interference fit forsecurement into the respective vertebra.

U.S. Pat. No. 4,355,429 to Mittelmeier, et al. discloses a slideprosthesis for the knee joint which is secured without cement. Anchoringpins are integrally provided and refer to by reference numerals 21 and22 and have a profile-like out of a bone screw. These pins are insertedinto slightly undersized holes drilled into the bone. If desired, thecontact surface may be covered with a coating of bio-active particles.In this patent, the prosthesis is made of carbon fiber, reinforcedplastics or aluminum oxide ceramic covered with bio-active particles.There is no disclosure of covering of the bone engaging surfaces of theprosthesis with a porous coating material. There is no disclosuretherein of a specific design for a spectrum of contact stress nor is asequence of interference giving away to durable ingrowth fixationdescribed.

SUMMARY OF THE INVENTION

As such, an invention has been disclosed herein which overcomes thedrawbacks of the prior art as described above by providing the followingcombination of features:

(A) The prosthesis interface surface of the present invention iscomposed of a multiplicity of modified conical projections located inclose proximity to one another and with substantially parallellongitudinal axes. The conical projections may have either a convex,concave or a straight profile and the dimensions thereof may be variedaccording to the particular application. Generally speaking, the axiallength of the conical projections should be greater than the diameter ofthe base portions thereof and this configuration will give the entireprosthesis interface surface a multiple spike-like geometry.

(B) The entire prosthesis interface surface including both the conicalprojections and the areas between the conical projections is coated withor alternatively is made from a porous material with the pores thereofbeing specifically selected to optimize bony ingrowth of bone tissue.The combination of the plurality of conical projections and the poroussurface not only facilitates the immediate stability of the prosthesisbut optimizes porous ingrowth by achieving a substantially greatercontact surface area than presently known.

(C) The stability of the prosthesis interface surface results from itsdesign geometry as well as from the specific technique of insertionthereof. In this regard, one aspect of the invention lies in the use ofa pilot driver including conical projections corresponding to theconical projections of the implant but slightly smaller inconfiguration. The pilot driver is impacted into the bone by a suitabletool to thereby produce slightly undersized conical spaces. When theimplant is then impacted with the respective conical projections beingforcibly inserted into the respective undersized conical recesses. Theinterference fit thereby created provides immediate stability.

(D) In cases where the areas of sclerotic hard bone are present on thebone interface surface so as to prevent the utilization of the pilotdriver, a modified drill guide may be utilized which instead ofincluding undersized conical projections rather includes drill holeguides which correspond to the proposed locations of the conicalprojections of the implant. When this drill hole guide is used, slightlyundersized drill holes may be made therethrough and into the boneinterface surface so that the prosthetic implant may be impacted ontothe surface and attached thereto with an appropriate interference fit.

The prosthetic interface surface of the present invention provides anumber of significant advantages over prior art designs:

(1) The surface provides immediate stability from implantation whichpromotes bony ingrowth.

(2) The prosthetic interface surface provides a large contact surfacethrough the use of conical projections to optimize bony ingrowth anddistribute stress evenly across the entire interfacial region.

(3) The prosthetic interface surface does not use cement andconsequently avoids all of the disadvantages of using methylmethacrylate cements with their high temperature curing characteristicsand thereby may avoid undue bone stresses during the curing and thusprovide a longer lasting implant.

(4) The surface configuration disclosed herein provides a spectrum,scale, array or gradient of contact stress to the patient's trabecularbone to optimize ingrowth effectiveness and promote stress-inducedstrengthening of the supporting trabecular bone. As described, the pointof each of the cones provides a very small surface area so that witheven moderate forces imposed thereon, the contact stress (or force perunit area) is very great at that region. The base of the cones and thearea between the cones has a large surface area such that with similarimposed forces to the moderate forces described above, the contactstress in this region would be quite small by comparison. Bone cannottolerate excessively large contact stresses and it also tends to recedeor atrophy in the face of excessively small contact stresses imposedthereon. The provision of a scale or gradient of contact stress assuresthat a considerable proportion of the working surface of the prostheticimplant will be at the optimal stress level. In this situation, the bonetissue picks out the region on the conical protrusions thereof which hasthe most desirable stress level and ingrows there and strengthens therewith time, while ingrowing at other regions of the implant to a somewhatlesser extent. The concept disclosed components incorporating thepresent invention therewith.

(5) The method of implantation of a prosthesis including the surface ofthe present invention is simplified which would reduce the probabilityof technical errors and may also reduce operating time.

(6) Since the prosthetic interface surface is designed primarily fornon-cemented implants, surface preparation is simplified.

(7) In conjunction with (6) above, the lack of cement reduces thesacrifice of trabecular bone which would ordinarily be necessary toprovide a recess for the cement.

Several modifications may be made to the teachings of the presentinvention without departing from the intended scope thereof. Forexample, the size of the conical projections as well as their profile,whether straight, concave or otherwise, may be altered to optimizeinsertion thereof or stability. Further, the prosthetic interfacesurface may be made porous by any technique available to manufacturers,such as, for example, sintering, fiber incorporation, ceramic coating,micro pore dusting and any other manufacturing technique. If desired,the prosthetic interface surface could also be used where appropriate intotal or partially cemented applications. It is to be noted in thisregard that this is a peripheral purpose of the present invention whichis mainly to be used without cement as described herein. Further, ifdesired, the prosthetic interface surface may also be used for theimplantation of tendons, ligaments or dentures.

Accordingly, it is a first object of the present invention to provide animproved prosthesis interface surface usable with any implantablecomponents where stable, long lasting fixation to bone is needed.

It is a further object of the present invention to provide an improvedprosthetic interface surface which includes a plurality of substantiallyconical protrusions designed to increase the surface area of theprosthetic interface with the bone.

It is a further object of the present invention to provide an improvedprosthetic interface surface which includes a porous surface tofacilitate bony ingrowth and thereby facilitate retention of theprosthetic implant.

It is a yet further object of the present invention to provide theporous surface by coating a base therewith.

It is a yet further object of the present invention to provide animproved prosthetic interface surface which enables the combination ofboth an interference fit and bony tissue ingrowth thereto.

It is a yet further object of the present invention to provide aninterface surface usable with prosthetic implants which provides aspectrum, scale, array or gradient of contact stress to the trabecularbone in which it is installed, thereby allowing the bone tissue tochoose the region on the interface surface having the optimum stresslevel, at which region the bone tissue will ingrow thereon andstrengthen over time.

It is a still further object of the present invention to provide a newimproved method of implanting a prosthesis including the surface of thepresent invention.

It is a yet further object of the present invention to provide such amethod which includes the use of a special pilot driver includingconical projections slightly smaller than the prosthesis projections toenable the above described interference fit.

It is a yet further object of the present invention to provide a furthermethod of implantation including the use of a drill hole guide insituations where areas of sclerotic hard bone are present on the boneinterface surface.

These and other objects, advantages and features of the presentinvention may be better understood by reading the following detaileddescription of the preferred embodiments in conjunction with theappended drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a total knee prosthesis includingfemoral component, tibial component and patella component, each of whichincorporates the present invention therein.

FIG. 2 shows a perspective view in the direction of the posteriorcondylar surface of a femoral component in accordance with the presentinvention.

FIG. 3 shows a perspective view in the direction of the patella-femoralflange of the femoral component also shown in FIG. 2.

FIG. 4 shows a side view of the femoral component of FIGS. 3 and 4.

FIG. 5 shows a cross-sectional view along the line 5--5 of FIG. 3.

FIG. 6 shows an enlarged perspective view of one of the fins shown inthe femoral component of FIGS. 3-5.

FIG. 7 shows a front view of the tibial component shown in FIG. 1.

FIG. 8 shows a bottom view of the tibial component shown in FIG. 1.

FIG. 9 shows a single substantially conical pin used in one embodimentof the present invention.

FIG. 10 shows a side view of a pilot driver designed to make pilot holesprior to insertion of the tibial component shown in FIGS. 1, 7 and 8.

FIG. 11 shows a bottom view of the tibial pilot driver of FIG. 10.

FIG. 12 shows a pin utilized in conjunction with the tibial pilot driverof FIGS. 10 and 11.

FIG. 13 shows a top view of a drill guide designed for use with thetibial component described in FIGS. 1, 7 and 8 in situations where thebone is sufficiently hard to preclude use of the tibial pilot driver ofFIGS. 10-12.

FIG. 14 shows a cross-sectional view through the line 14--14 of FIG. 13.

FIG. 15 shows a perspective view of the present invention when used inconjunction with an acetabular component.

FIG. 16 shows a cross-sectional view through the line 16--16 of FIG. 15.

SPECIFIC DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a total knee prosthetic replacement including a patellarcomponent 10, a femoral component 20 and a tibial component 60. Withreference to FIGS. 2-6, the details of the femoral component will be setforth, with it being clearly understood that the details of the presentinvention as applied to the femoral component are applicable to any bodyimplant. The femoral component 20 is seen to include a patella-femoralflange 21 and vertical condylar extensions 23. In the interior of thecomponent, an interface surface is provided formed at least partially ofa flat surface 25 is provided which is connected to a substantially flatinterior surface 29 of the patella-femoral flange 21 by an angular innersurface 27. On the other side of surface 25, the interface surfacecontinues with each of the vertical condylar extensions having an angledsurface 31 and a further surface 33 substantially parallel to the abovementioned surface 29 on the patella-femoral flange 21. Surfaces 27 and31 each form obtuse angles where they meet surface 25. As is seenespecially in FIGS. 2, 3 and 4, the surfaces 25, 27 and 31 can be seenas respective subregions of a first type of interface surface becausethey are each provided with a plurality of conical projections 35extending therefrom. As best seen in FIG. 4, the conical projections 35on the surface 25 extend directly upwardly and each conical projection35 includes a central axis 37 which is substantially parallel to theaxes 37 of all other conical projections 35. Also, as best shown in FIG.4, the projections 35 on the respective surfaces 27 and 31 also includeaxes 37 which are substantially parallel to the axes 37 on allpreviously mentioned conical projections 35. In order to maintain theaxes 37 on the conical projections 35 which are mounted on the surfaces27 and 31 parallel with the axes 37 on the conical projections on thesurface 25, the projections 35 on the inclined surfaces 27 and 31 appearto be at least partially embedded into the respective surfaces 27 and31. As such, while the conical projections 35 on the surface 25 includeside wall portions 39 and 41 of substantially equal length, the conicalprojection 35 on the angled surface 27 include surfaces 39' and 41'which differ in length, and similarly, the conical projections 35 on theangled surface 31 include surfaces 39" and 41" of differing lengths.This configuration enables the axes 37 of all of the conical projections35 to be substantially parallel to one another.

It has been determined that the surfaces 29 and 33 of the respectivepatella-femoral flange and vertical condylar extensions should alsoinclude surface projections to enhance the retention of the femoralcomponent on the end of the femur. However, due to the fact that thesurfaces 29 and 33 are substantially parallel to the direction in whichthe component is impacted into its installed position, substantiallyconical projections may not be used on the surfaces 29 and 33. As such,instead, fins 43 are employed for these surfaces. FIG. 6 shows a singlefin 43 protruding from a surface, for example, the surface 33, a smallportion of which is shown in FIG. 6. The fin 43 includes a substantiallytriangular base portion 45 defined by two sides 47 of the fin, and theface of the surface 33. The uppermost portion of the fin 43 is definedby a substantially pointed area 49 which connects with the faces 47 ofthe base 45 by way of substantially triangular faces 51. The triangularfaces 51 merge together at an intersecting linear portion 53 whichconnects the points 48 and 49 together. Since the point 48 is on surface27, or one of surfaces 31, but is spaced from surface 33, and the point49 is on the surface 33, the linear portion 53 is wedge-like andprovides a wedging action with the bone surface when the femoralcomponent 20 is installed thereon. This second type of projectiontherefore communicates with surface 33 of the interface surfacethroughout its length. As will be further explained hereinafter, thefemoral component 20 is installed onto the end of the femur bone byforcing it thereon with a linear motion. Prior to the installation ofthe femoral component 20 onto the femur, the end of the femur isprepared for such installation through the forming of pilot holesdesigned to provide an interference fit with the conical projections 35and pilot recesses designed to provide an interference fit with the fins43. The process of forming such holes and recesses will be furtherdescribed in conjunction with the specific description of the tibialcomponent 50 below. FIG. 5 shows a cross-sectional view through thepatella-femoral flange 21 and shows a cross-section through the fins 43.As shown in FIG. 5, the surfaces 51 and the linear portion 53 form, withthe surface 33, a substantially triangular configuration which, as willbe better understood in conjunction with FIG. 6, decreases in size asone moves upwardly toward the point 49.

Referring now to FIGS. 1 and 7-14, the details of the tibial component60 and its method of installation will be described. With reference toFIGS. 7 and 8, the tibial component 60 is seen to include a top surface61 designed for bearing engagement with the outer surface of the femoralcomponent 20, and further includes a bottom surface 63. As best seen inFIG. 8, the tibial component 50 is approximately U-shaped with legs 65connected together by connecting portion 67. The bottom surface 63includes a large number of substantially conical projections 69 each ofwhich having an axis 71 with the axes 71 being substantially parallel toone another. The parallel nature of the axes 71 enables the tibialcomponent to be installed on a bone surface of the tibia by linearlyforcing the substantially conical projections 69 into pre-formedsubstantially conical holes in the bone surface which are made slightlysmaller than the substantially conical projections 69 to ensure aninterference fit therein. At this point, it is noted that the conicalprojections 69 of the tibial component 60, the substantially conicalprojections 35 and fins 43 of the femoral component 20, and all othersuch substantially conical projections and/or fins as contemplated bythe present invention each have on the surface thereof a porous materialspecifically designed to enhance bony ingrowth therein to assist inmaintaining the respective prosthetic components in their originallymounted positions. In this regard, the surfaces thereof may be madeporous by any technique desired, such as, for example, sintering, fiberincorporation, ceramic coating, micro pore dusting and any other desiredmeans. Further, it is noted, that the substantially conical projectionsand/or fins may be entirely made of a material which is porous innature, if desired.

If desired, the tibial component 60 shown in FIGS. 7 and 8 may be madeof a single forged or molded piece including the projections 69 as anintegral part of the molding. Alternatively, in situations where conicalprojections 69 of differing configurations for differing situations maybe required, the substantially conical projections 69 may be formed asseparate entities insertable into holes (not shown) in the bottom 63 oftibial components 60. In this vein, attention is directed to FIG. 9which illustrates a typical substantially conical projection 69. As seenin FIG. 9, the projection 69 includes the above described axis 71 and isformed as an integral part of a base portion 73. The base portion 73includes a substantially cylindrical wall 75 and a flat wall 79connected thereto through a substantially conical wall 77. Thesubstantially conical projection 69 protrudes from a substantially flatsurface 81 and is seen to include an annular radiused portion 83emerging from the surface 81 which itself merges into a conical surface85 which merges into a radiused, substantially semi-spherical tipportion 87. The holes formed in the surface 63 of the component 60 aremade slightly smaller in diameter than the base portion 73 of the member69 so that the member 69 may be inserted into these openings (not shown)in a press-type fit. As shown in FIG. 9, the surface formed by theportions 83, 85 and 87 of the substantially conical projection 69 isporous in nature so as to enhance the ingrowth of bony tissue asexplained above.

With reference now to FIGS. 10, 11 and 12, a pilot driver 100 is shownwhich may be used to create the pilot holes within the bone tissue whichare necessary to enable insertion of the substantially conicalprojections of the tibial component 60. The pilot driver 100 includes abottom surface 101, a top surface 103 and a post-like member 105extending outwardly from the top surface 103. The post-like member 105is provided so that the pilot driver 100 may be attached to a suitabledevice which will enable the pilot driver 100 to be impacted against thedesired bone tissue so as to create the pilot holes for thesubstantially conical projections of the tibial component 60. As bestshown in FIG. 10, the bottom surface 101 includes a plurality of pins107 of slightly smaller dimension than the substantially conicalprojections 69 of the tibial component 60 so that the substantiallyconical projections 69 will form an interference fit with the holesformed by the projections 107. As best seen in FIG. 11, the bottomsurface 101 has approximately the same configuration as the bottomsurface 63 of the tibial component 60. This bottom surface 101 includesleg portions 109 connected together by connecting portion 111. Member105 may be made of any cross-section enabling it to be connected to anappropriate impacting tool, such as, for example, round, square,hexagonal, etc. The projections 107 may be formed integrally with thepilot driver 100, or alternatively, the projections 107 may be formed asseparate pins insertable into holes (not shown) in the surface 101 ofthe pilot driver 100. In this regard, references made to FIG. 12 whichshows a typical pilot driver pin 107. The pin 107 includes a baseportion 113 including a substantially cylindrical outer surface 115which surface 115 is connected to a flat bottom surface 119 through asubstantially conical surface 117. The base poriton 113 includes a topsurface 121 which merges with the projection at an annular radiusedportion 123. The above described structure is substantially identical tothe corresponding structure of the base portion 73 of the substantiallyconical projection 69 described above. The annular radiused portion 123merges into a substantially conical portion 125 of the projection 107and is made of substantially the same angular configuration as thesubstantially conical projection 69 discussed above. The portion 125terminates at a sharp point 127 as contrasted with the rounded end 187of the substantially conical projection 69. This pointed end 127 enablesthe projection 107 to form an opening of similar configuration in thebone tissue when impacted therein by a suitable device (not shown) theangle of the surface 125 being similar to the angle of the surface 85 ofsubstantially conical projection 69 enables the substantially conicalprojection 69 to fit into the hole formed by the projection 107 with aninterference type fit the interference of which is increased as theprojections 69 are pushed further and further into the holes formed bythe projection 107. It is noted that the concepts taught by the pilotdriver 100 which is specifically designed to form pilot holes forreceipt of the projections on a tibial component 60 may also beapplicable to any pilot driver designed for any implantable prostheticcomponent, such as, for example, an acetabular component, a patellarcomponent or a femoral component. The main thing that all pilot driversmust have in common is the placement of projections so as to enableforming holes in bone tissue through linear movement thereof only.

Under certain circumstances, the bone tissue in the region where thecomponent is to be implanted is to hard too enable the successful use ofthe pilot driver. In the case of the tibial component, this problemwould be remedied through the use of a tibial drill guide illustrated inFIGS. 13 and 14. The tibial drill guide 130 shown in FIGS. 13 and 14 isbasically a template with holes in it which allow accurate location ofpilot holes for tibial component projections 69. The drill guide 130includes a top surface 131, a bottom surface 133, and a peripheral edge135. As best shown in FIG. 13, the top surface 131 as well as the bottomsurface 133 are made of approximately the same configuration as thesurface 63 of the tibial component 60 and includes leg portions 137connected by a connecting portion 139. The drill guide 130 includes aplurality of holes 141 extending therethrough and of a diameter enablingextension therethrough of a drill bit of appropriate size to drillsubstantially conical holes within the hard bone tissue which willenable the projections 69 of the tibial component 60 to fit therein withan interference fit. In use, the tibial drill guide 130 is placed overthe region where the holes are to be drilled and is fastened there byany suitable means. After the drill guide 130 is fastened into position,the holes are drilled after which the tibial component 60 is impactedlinearly into its fixed position. It is noted, that the concepts taughtby the tibial drill guide 130 are equally applicable to a drill guideformed to make holes for receipt of substantially conical projections inany implantable prosthetic component.

FIGS. 15 and 16 illustrate a further embodiment of the presentinvention, which is intended to be used in conjunction with anacetabular component, more commonly known as a hip socket replacementjoint. Referring to FIGS. 15 and 16, the acetabular component 150 isseen to comprise a substantially semi-spherical surface 151 whichcomprises a porous surface to enhance ingrowth of bone tissue therein.In the preferred embodiment, the porous surface comprises a porous layerof an alloy including a combination of titanium, aluminum and vanadiummarketed under the registered trademark Tivanium by Zimmer,Incorporated. As shown, the surface 151 has extending outwardlytherefrom, a series of rings of conical projections 153 each of whichhas an axes 155 therethrough. The conical projections in this embodimentof the invention are generally similar to those shown in the embodimentof FIGS. 1-5 in that some such projections are entirely exposed, othersappear partially embedded, and others communicate with the surface 151throughout their longitudinal length. As best seen in FIG. 16, the axes155 of the respective substantially conical projections 153 aresubstantially parallel to one another so that the acetabular component150 may be inserted into the associated bone tissue by a linear motionthereof to thereby cause an interference fit between the respectivesubstantially conical projections 153 and holes formed in the bonytissue for receipt of this substantially conical projections 153.

As best seen in FIGS. 15 and 16, in order that the axes 155 may beparallel, the rings of substantially conical projections take ondiffering configurations with increasing circumference. As shown in FIG.15, in the ring 157 the projections 153 are substantially fully exposedwhile in the ring 165, the projections 153 are as the fins describedhereinabove in that they taper longitudinally and are at least partiallylaterally embedded substantially throughout their lengths within thesurface 151. If desired, the projections of the larger rings 163, 165may be replaced with fins having triangular configurations similar tothose fins 43 disclosed in conjunction with the femoral component 20shown in FIGS. 2-6.

As above, the acetabular component may be installed by forming holes inthe bone tissue with either (1) an acetabular pilot driver (not shown);and or (2) an acetabular drill guide and a drill with appropriatelysized drill bit and (not shown)., and subsequently linearly forcing theprojections 153 into the holes with an interference fit.

The prosthetic interface surface has been disclosed herein in terms of aplurality of conical protrusions each shown in the drawings to include asubstantially circular base portion and converging to a radiused tipportion. It is noted here, that this construction of the protrusions ismerely one example of the possible configurations of the protrusionswhich may be utilized within the purview of the present invention. To bewithin the purview of the present invention, the protrusions mustinclude (1) a base portion of any shape, (2) a body portion converginglytapering away from the base portion, and (3) a tip portion having asmaller area than the area of the base portion. Further the longitudinalaxes of all of the protrusions must be substantially parallel to oneanother. As such, the base portion may be elliptical, polygonal (with3-12 or more sides) or any irregular shape, the body portion may includea flat, concave or convex surface or any combination thereof and the tipportion may be flat to provide a truncated protrusion or as well couldbe substantially pointed, or of any other configuration, such as,concave or convex. Thus, the protrusions may each comprise a rightcircular cone, truncated or otherwise, a pyramid with any desired numberof sides, truncated or otherwise, an elliptical cone, truncated orotherwise, or any other configuration having the above described threecriteria, truncated or otherwise. Alternatively, respective protrusionsmay each have a unique one of the above described configurations withseveral configurations being represented on a given prosthesis. Wherenecessary, the pilot driver and/or drill guide disclosed herein may beappropriately modified to allow the formation of the appropriate holesin the bone tissue for receipt of the various above described potentialshapes and configurations for the protrusions.

It is stressed here, that the above described embodiments of prostheticimplants utilizing the interface surface of the present invention are tobe considered merely examples of the uses to which the inventive surfacemay be put. The interface surface may be used with any implantableprosthesis where the goal is a permanent fixation through bony ingrowththerein. The prosthesis incorporating the inventive surface thereonrequire no cement for fixation and may easily be installed with lesssurgical time than is normally required for cemented and other implants.As such, various modifications, changes or alterations of the inventiondisclosed herein may become evident to those skilled in the art and theinvention disclosed herein is not intended to be limited by thedescription hereinabove but rather, is intended only to be limited bythe appended claims.

We claim:
 1. A prosthetic kit having a prosthetic kit for engaging couplingly with bone tissue of a living being, the prosthetic member comprising:an interface surface for communicating with the bone tissue, said interface surface having a plurality of apertures therein; and a plurality of projection members each formed of a projection portion and an integral base portion aligned therewith along a longitudinal axis of said projection member, said base portion being press fitted into an associated aperture in said interface surface whereby said projection portion extends outwardly of said interface surface, said longitudinal axis of said plurality of projection members being substantially parallel to one another.
 2. The prosthetic member of claim 1 wherein there is further provided pilot driver means having a plurality of driver projection members arranged thereon and in an array configuration which corresponds to an array configuration of said projection members projecting from said interface surface, for preforming respective accommodating openings in the bone tissues.
 3. The prosthetic member of claim 2 wherein said driver projection members are dimensioned to be smaller than their corresponding projection members to permit an interference fit between said projection members and said preformed openings in the bone tissue.
 4. The prosthetic member of claim 2 wherein said projection members and said driver projection members each have a predetermined tapering shape, in a direction outwardly along a longitudinal axis thereof.
 5. The prosthetic kit of claim 1 wherein there is further provided drill guide means having a plurality of through-holes arranged in an array configuration which corresponds to an array configuration of said projection members projecting from said interface surface, for preforming respective accommodating openings in the bone tissue.
 6. A prosthetic implant system comprising:a prosthetic member having an interface surface and a plurality of substantially conically-shaped projection members, each being substantially parallel to one another, extending therefrom, for engaging couplingly with a bone tissue of a living being; and a pilot member having means for defining locations on said bone tissue of said living being corresponding to desired holes therein for accommodating respective ones of said projection members, said pilot member being provided with a plurality of driver projection members extending therefrom, each having a substantially conical configuration and dimensioned to be smaller than a corresponding one of said projection members for forming a pilot hole in said bone tissue of said living being in response to an impact force applied to said pilot member.
 7. The prosthetic implant system of claim 6 wherein said interface surface is porous.
 8. The prosthetic implant system of claim 6 wherein said projection members each have a porous surface.
 9. A method of installing a prosthetic implant, the method comprising the steps of:shaping a region of bone tissue of a living being to conform to a shape defined by an interface surface of the prosthetic implant; aligning a pilot driver having a plurality of driver projections whereby said driver projections are situated at selected locations on said bone tissue; urging said pilot driver toward said bone tissue whereby said driver projections form said plurality of holes; and urging said prosthetic implant into engagement with said shaped region of said bone tissue whereby said integrally formed projection members are driven into direct communication with said bone tissue at respectively associated ones of said holes, whereby an interference fit between said integrally formed projection members and said bone tissue, having a pressure gradient, is achieved in each hole.
 10. The method of claim 9 wherein said plurality of holes have respective central axes substantially parallel with one another, said plurality of projection members have respective longitudinal axes substantially parallel with one another, and said step of urging comprises the step of impacting said bone tissue and said prosthetic implant toward one another in a direction whereby said respective central axes are substantially parallel and aligned with said respective longitudinal axes. 